Add "--with-base-isa" support to autoconf

This allows someone to build a RV32I toolchain without going in and
messing with the Makefile directly.

Makefile.in

@@ -16,6 +16,7 @@ glibc_url := $(GNU_MIRROR)/glibc/glibc-$(glibc_version).tar.gz
 newlib_url := ftp://sourceware.org/pub/newlib/newlib-$(newlib_version).tar.gz
 
 XLEN ?= @XLEN@
+BASE_ISA ?= @BASE_ISA@
 SYSROOT := $(INSTALL_DIR)/sysroot
 
 SHELL := /bin/sh
@@ -159,7 +160,8 @@ stamps/build-gcc-linux-stage1: src/gcc stamps/build-binutils-linux \
 		--disable-libgomp \
 		--disable-nls \
 		$(MULTILIB_FLAGS) \
-		--disable-bootstrap
+		--disable-bootstrap \
+		--with-arch=RV$(XLEN)$(BASE_ISA)
 	$(MAKE) -C $(notdir $@) inhibit-libc=true all-gcc
 	$(MAKE) -C $(notdir $@) inhibit-libc=true install-gcc
 	$(MAKE) -C $(notdir $@) inhibit-libc=true all-target-libgcc
@@ -182,7 +184,8 @@ stamps/build-gcc-linux-stage2: src/gcc stamps/build-glibc-linux$(XLEN) \
 		--disable-libquadmath \
 		--disable-nls \
 		$(MULTILIB_FLAGS) \
-		--disable-bootstrap
+		--disable-bootstrap \
+		--with-arch=RV$(XLEN)$(BASE_ISA)
 	$(MAKE) -C $(notdir $@)
 	$(MAKE) -C $(notdir $@) install
 	mkdir -p $(dir $@) && touch $@
@@ -222,7 +225,8 @@ stamps/build-gcc-newlib: src/newlib-gcc stamps/build-binutils-newlib
 		--disable-libssp \
 		--disable-libquadmath \
 		--disable-libgomp \
-		--disable-nls
+		--disable-nls \
+		--with-arch=RV$(XLEN)$(BASE_ISA)
 	$(MAKE) -C $(notdir $@) inhibit-libc=true
 	$(MAKE) -C $(notdir $@) install
 	mkdir -p $(dir $@) && touch $@

configure.ac

@@ -56,6 +56,13 @@ AC_ARG_WITH(xlen,
 	AC_SUBST(XLEN, 64)
 	)
 
+AC_ARG_WITH(base-isa,
+	[AS_HELP_STRING([--with-base-isa=G/I],
+		[Sets the base RISC-V ISA to either G or I, defaults to G])],
+	AC_SUBST(BASE_ISA, $withval),
+	AC_SUBST(BASE_ISA, G)
+	)
+
 AC_ARG_ENABLE(atomic,
 	[AS_HELP_STRING([--disable-atomic],
 		[disable use of atomic memory instructions in glibc @<:@--enable-atomic@:>@])],